1. Technical Field
The present invention relates to a laser scanning optical system for deflecting a linearly-polarized light beam so as to scan an imaging surface with the linearly-polarized light beam via at least one scanning optical element.
2. Description of Related Art
In the field of such laser scanning optical systems, conventionally, shading corrections, which are methods for correcting uneven intensity distribution on an imaging surface, have been proposed, for example, by Japanese Patent Laid-Open Publication No. 2-035143, Japanese Patent Laid-Open PublicatiNo.2005-326744, Japanese Patent Laid-Open Publication No. 2002-182143 and Japanese Patent Laid-Open Publication No. 2009-169248. According to the methods proposed by these documents, the polarization state of a light beam entering a scanning optical element is defined, and the transmittance property of the scanning optical element (when the scanning optical element is a lens) or the reflectance property of the scanning optical element (when the scanning optical element is a reflector) is optimized so that the uneven intensity distribution can be suppressed.
If an optically-anisotropic matter is placed in an optical path of a conventional laser scanning optical system, between a deflector and the scanning optical element, the polarization state of the light entering the scanning optical element is mostly different from the polarization state of the light emitted from the light source, due to the birefringence effect of the optically-anisotropic matter.
It is conceivable that the strength of the birefringence effect of the optically-anisotropic matter on the light varies, depending on the state of the optically-anisotropic matter or the position of the optically-anisotropic matter where the light passes, and therefore, it is difficult to accurately estimate the change of the polarization state. Therefore, even in a laser scanning optical system that is so designed that uneven intensity distribution can be suppressed while the light is in an expected polarization state, if the polarization state of the light changes beyond expectation, the uneven intensity distribution may not be suppressed.